Conventional scuba diving masks, for example, can often be retrofitted with corrective lenses to accommodate scuba divers who may need to compensate for their poor eyesight during underwater activities.
Such masks typically have a frame with two relatively rigid rings, circular or non-circular rings joined to one another by a bridge configured for positioning over a user's nose. The internal contour of each ring is provided with flanges for engaging “visors”, i.e., transparent lenses that allow the user to see underwater. The visors are held in position by retaining collars that replicate the internal contour of the rings and may be attached to the frame, either removably or permanently, using suitable fasteners.
In other scuba diving masks suitable for fitting with corrective lenses, the same lens can generally be mounted on both the right side and left side of the mask, by simply rotating the lens about an axis perpendicular to the plane of the lens. Generally speaking, the lenses are symmetrical to avoid obliging retailers to keep double sets of right-hand and left-hand lenses. As a result, manufacturers usually provide retailers with the operative components of each diving mask separately, that is, they supply the diving masks without lenses together with a set of corrective lenses, so that the retailers can later select the appropriate combination of lenses for the masks to suit a particular customer's requirements, e.g., eyeglass precription. Alternatively, this type of mask can be fitted with ordinary lenses, as is appreciated by those skilled in the art.
The assembly or replacement of lenses by the retailer, however, requires suitable equipment, which generally comprises a dedicated tool—a basic screwdriver, in many cases—by which the retaining collars are separated from the mask frame in order to install or replace a lens. Typically, the retailer is instructed suitably to perform these operations without damage to lenses e.g., scratching, or to the mask frame. However, as the dedicated tool is generally harder than the lens or the frame, and because personnel performing the installation are not always adequately trained or sufficiently experienced, there is still significant risk of mask damage.
Moreover, when lenses are installed or replaced by the end user, without the use of a dedicated tool and/or the necessary experience, there is a significantly greater risk of damaging the lenses or frame. Indeed, the action of replacing a lens, and even more of installing a lens, carries an additional risk of damage to the lip of the skirt located between the frame and the lens, with the resulting loss of watertightness of the mask. This problem has also been experienced where a mask is equipped with ordinary lenses and replacement of a damaged “visor ”is desired.